Lung infections are a major cause of morbidity and mortality worldwide. Serious lung infections lead to respiratory distress syndrome for which there is no specific treatment available. In the wake of rise in lung infections caused by multi-drug resistant pathogens and unavailability of a wonder-drug to control associated inflammation, it is important to develop novel therapies. An ideal therapeutic would be the one that can suppress the inflammatory response but preserve the anti-pathogen host defense and lung homeostasis. Our long term goal is to develop therapies based on boosting the natural host defense mechanisms mediated by pathogen-recognition receptors. Surfactant protein (SP)-A and Toll-like receptor (TLR) are known as secretory and signaling pathogen-recognition receptors, respectively. Interaction between SP-A and TLR4 inhibits the TNF-? response but preserves the phagocytic activity of antigen-presenting cells. Thus, a TLR4-interacting region of SP-A, mimicking these properties of SP-A may be developed into a novel SP-A-based immunotherapeutic. Using cutting-edge technology, we have recently identified a TLR4-interacfing region of SP-A (SPA4 peptide). The objective of this application is to define the biological relevance and determine the mechanism of action of SPA4 peptide. We hypothesize that the SPA4 peptide will inhibit TLR4-induced inflammation, while maintaining TLR4-mediated bacterial-phagocytosis and clearance. The specific aims are to: (1) determine if SPA4 peptide inhibits inflammatory responses and improves clinical symptoms in an animal model of lung inflammation, (2) determine if SPA4 peptide inhibits the inflammatory response and maintains the phagocytic response at a cellular level, and (3) assess the biological effects of SPA4 peptide in clinically-relevant animal models of lung infection and inflammation. This project is innovative because it uses a unique concept of developing an immunotherapeutic that will not only control inflammation, but also help maintain anti-pathogen responses and lung homeostasis. It is expected that an SP-A-based therapeutic will have a significant impact on improving lung health during infection and inflammation.